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What's the difference between asymptomatic and pre-symptomatic spread? And does it matter with coronavirus?

CNN's Dr. Sanjay Gupta reports.

Posted: Jun 10, 2020 1:01 AM
Updated: Jun 10, 2020 1:01 AM

This novel coronavirus is bizarre for many reasons, making its spread unpredictable and hard to control.

One oddity is how easily people can get infected by someone without symptoms. But there's a difference between asymptomatic spread and pre-symptomatic spread.

Here's what you need to know:

Asymptomatic spread is the transmission of the virus by people who do not have symptoms and will never get symptoms from their infection. But those infected carriers could still get others very sick.

Pre-symptomatic spread is the transmission of the virus by people who don't look or feel sick, but will eventually get symptoms later.

How can I tell if someone is pre-symptomatic or asymptomatic?

You can't. Both types of carriers look and feel normal, though the pre-symptomatic carriers will get symptoms later.

Studies suggest pre-symptomatic spread is more common than asymptomatic spread.

"Detailed contact tracing from Taiwan as well as the first European transmission chain in Germany suggested that true asymptomatics rarely transmit," said Babak Javid, a principal investigator at Tsinghua University School of Medicine in Beijing and an infectious disease consultant at Cambridge University Hospitals.

"However, those (and many other) studies have found that paucisymptomatic transmission can occur, and in particular, in the German study, they found that transmission often appeared to occur before or on the day symptoms first appeared."

How is it possible to spread coronavirus without symptoms?

"When you speak, sometimes you'll spit a little bit," said Anne Rimoin, an epidemiology professor at UCLA's School of Public Health.

"You'll rub your nose. You'll touch your mouth. You'll rub your eyes. And then you'll touch other surfaces, and then you will be spreading virus if you are infected and shedding" the virus.

How many people get infected by someone without symptoms?

The US Centers for Disease Control and Prevention estimates 40% of coronavirus transmission happens before people feel sick.

In one study, about 4 in 5 people with confirmed coronavirus in China were likely infected by people who didn't know they had it, according to research published in the journal "Science."

"These findings explain the rapid geographic spread of (coronavirus) and indicate containment of this virus will be particularly challenging," researchers wrote.

Many people with coronavirus have no idea they have it -- either because they're asymptomatic, pre-symptomatic, or paucisymptomatic (meaning they have extremely mild symptoms).

The CDC said almost half of the 712 people with coronavirus who were on the Diamond Princess cruise ship didn't have any symptoms when they tested positive.

And a study from Iceland showed 50% of those who tested positive had no symptoms at the time of testing.

How can so many people have or spread coronavirus with no symptoms (yet)?

This coronavirus has a lengthy incubation period -- the time between when someone gets infected to when they start showing symptoms (if they get symptoms at all).

The flu can also be spread without symptoms, but the incubation time is much shorter -- typically one to four days, with symptoms often showing up within two days after infection, the CDC says.

With coronavirus, the incubation period is about three to 14 days, with symptoms typically appearing "within four or five days after exposure," according to Harvard Medical School.

"We know that a person with COVID-19 may be contagious 48 to 72 hours before starting to experience symptoms," Harvard experts wrote.

"Emerging research suggests that people may actually be most likely to spread the virus to others during the 48 hours before they start to experience symptoms."

Are pre-symptomatic carriers more contagious before or after they get symptoms?

"People tend to be the most contagious before they develop symptoms, if they're going to develop symptoms," CNN Chief Medical Correspondent Dr. Sanjay Gupta said.

"They call that the pre-symptomatic period. So people tend to have more virus at that point seemingly in their nose, in their mouth. This is even before they get sick. And they can be shedding that virus into the environment."

If I can't see who's pre-symptomatic or asymptomatic, how do I stay safe?

Wearing face masks and keeping a physical distance from others "can help reduce the risk that someone who is infected but not yet contagious may unknowingly infect others," the Harvard team said.

Indiana Coronavirus Cases

Data is updated nightly.

Confirmed Cases: 48524

Reported Deaths: 2698
CountyConfirmedDeaths
Marion11682684
Lake5180242
Elkhart330146
Allen2798132
St. Joseph196466
Cass16389
Hamilton1563101
Hendricks1410100
Johnson1288118
Porter73237
Tippecanoe7268
Madison65964
Clark65544
Bartholomew58644
LaPorte58026
Howard57757
Kosciusko5494
Vanderburgh5486
Marshall4904
Noble48228
Jackson4723
LaGrange4709
Hancock45035
Boone44543
Delaware44550
Shelby42625
Floyd38144
Morgan32931
Monroe30028
Grant29526
Montgomery29420
Clinton2892
Henry27415
Dubois2736
White26510
Decatur25032
Lawrence24625
Dearborn23823
Vigo2358
Harrison21822
Warrick21829
Unassigned193193
Greene18932
Miami1832
Jennings17611
Putnam1698
DeKalb1624
Scott1627
Daviess14317
Wayne1406
Orange13623
Perry1299
Steuben1292
Franklin1248
Jasper1212
Ripley1177
Wabash1122
Carroll1102
Fayette997
Newton9810
Starke933
Whitley925
Gibson812
Huntington812
Randolph794
Wells731
Fulton721
Jefferson722
Jay680
Washington671
Pulaski661
Knox640
Clay604
Rush583
Adams501
Owen491
Benton480
Sullivan451
Posey420
Brown391
Spencer381
Blackford372
Crawford320
Fountain322
Tipton321
Switzerland270
Parke230
Martin220
Ohio170
Vermillion140
Warren141
Union130
Pike110

Ohio Coronavirus Cases

Data is updated nightly.

Confirmed Cases: 57956

Reported Deaths: 2927
CountyConfirmedDeaths
Franklin10410429
Cuyahoga7883373
Hamilton6019198
Lucas2752302
Marion273438
Pickaway219741
Summit2143206
Montgomery203427
Mahoning1832232
Butler159944
Columbiana130760
Stark1123112
Lorain103567
Trumbull96770
Warren86021
Clark7669
Delaware58215
Fairfield57216
Tuscarawas56710
Belmont54922
Medina52332
Lake50018
Licking49312
Miami46631
Portage44258
Ashtabula43544
Wood42851
Clermont4146
Geauga40742
Wayne36351
Richland3455
Allen32141
Mercer2829
Greene2589
Darke25125
Erie24422
Holmes2363
Huron2202
Madison1978
Ottawa14923
Sandusky13614
Crawford1355
Washington13520
Putnam12815
Ross1273
Hardin12312
Morrow1161
Coshocton1112
Auglaize1074
Monroe8917
Jefferson882
Union861
Muskingum831
Hancock791
Hocking788
Guernsey743
Preble731
Lawrence710
Williams712
Clinton680
Shelby684
Logan621
Fulton610
Ashland591
Athens591
Carroll593
Wyandot596
Brown571
Defiance513
Knox511
Fayette460
Highland451
Scioto410
Champaign401
Perry351
Van Wert350
Seneca342
Henry300
Paulding250
Adams241
Jackson230
Pike230
Vinton222
Gallia181
Harrison121
Meigs120
Morgan110
Noble110
Unassigned00
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